Abstract

An understanding of animal time budgets is crucial to behavioural biology. Although many studies have analysed time budgets of individual species, only a few have made interspecific comparisons. Here we take an interspecific look at one part of the time budget, feeding time. We hypothesize that feeding time can be predicted by the amount of time an animal needs to reach satiation. This time should be equal to the ratio of handling time to digestion time. For 19 herbivorous species from insects to mammals, we calculate this ratio and compare it to the observed feeding time. The mean difference between calculated and observed values is small (a half hour per 24 h-day), indicating that herbivore feeding times can often be approximated by the ratio of handling time to digestion time. We make three points concerning the time allocated to feeding in herbivores based on this interspecific comparison. First, our analysis suggests that herbivores often feed to satiation, which could mean that they are often released from time constraints. It is also possible, however, that while herbivores have enough time to reach satiation, they do not necessarily have sufficient time to choose the most desirable diet. Wilson's principle of stringency theoretically supports the former interpretation. It suggests that animals experience periods in their life in which they are time-constrained but that these periods are the exception rather than the rule. Most optimal foraging studies have assumed the opposite. The second point of this paper is therefore a recommendation: to consider the possibility that animals may often be released from time constraints. The third and final point is that feeding time is independent of body mass in our analysis. This is because handling time scales with body mass according to a parameter that is similar to the one for digestion time, and feeding time can be approximated by the ratio of handling time to digestion time.